ocr: PROTON-PROION REACTION Ina profon-proton reaction, two protons col- lide and one becomes a neutron, which, to- gether with the proton, forms the heavy iso- tope of hydrogen called deuterium. Once again, a free proton collides with it. Now the result is the light helium 3 (helium minus one neutron). Next, two light helium nuclei fuse together, making one helium atom and two free protons. During this process 0.7 percent of the mass disappears'. Actually, according to the law E=mc the mass has not disap- peared, but has turned into energy.
